Method for producing reducible iron-containing material having less clustering during direct reduction and products thereof

Abstract: A method for abating the incidence of cluster formation of reducible iron-containing material during the direct reduction of said material is disclosed. The method generally comprises contacting the reducible iron-containing material with a cluster-abating effective amount of a dispersion of a particulate material.

Description: Background of the Invention The current invention relates to a novel process for lowering the incidence of clustering or sticking of reducible iron-containing material during the direct reduction of said material. The process comprises contacting the reducible iron-containing material prior to direct reduction thereof with a dispersion of at least one non-pozzolanic particulate material. It is a well-known technical problem that particulate reducible iron containing material tends to stick together, forming large clusters or agglomerates during their processing in a direct reduction furnace. These clusters tend to remain intact during treatment in a direct reduction furnace, impeding appropriate flow through the furnace. One possible though unacceptable solution to this problem is lowering the furnace temperature and through-put. From the perspective of efficiency alone this solution is not appropriate. Other solutions have been suggested to decrease clustering in a direct reduction furnace while maintaining a high processing rate through the furnace. For example, European Patent Specification No. 207 779 teaches application of a cement coating to the surface of burned iron ore prior to direct reduction in order to prevent agglomeration in the direct reduction furnace. US Patent No. 3,062,639 discloses a process for treating reducible iron oxide by contacting the iron oxide with a solution comprising an element selected from the group consisting of an alkali metal, an alkaline earth metal, a metal of group V, a metal of group VIB, boron, and silicon. This is intended to prevent clustering in the furnace reduction zone. US Patent No. 3,549,352 discloses a process for substantially suppressing bogging (clustering) in an iron ore reduction process by adding directly to a ferrous reduction bed a dry powder selected from alkaline earth metal oxides or carbonates, especially the oxides of calcium and magnesium. In US Patent No. 3,975,182, a method to produce iron oxide pellets which do not form clusters in a vertical shaft moving bed is disclosed. In that method, a surface coating of lime, limestone or dolomite is formed on iron oxide pellets. The lime-containing material is added in dry form in a balling machine with a spray of a little water to promote adhesion. The pellets are then fired to form a hard coating of calcium ferrite. DE-OS-2 061 346 discloses a process for reduction of iron ore pellets which consists of coating said pellets with a ceramic powder prior to introduction into the direct reduction furnace. A special adhesive may be sprayed on the pellets in order to promote the adhesion of the ceramic powder to the pellets. However, such above-mentioned solutions are not adequate to over-come ore clustering in direct reduction furnaces at the processing rates and conditions currently required. Accordingly, the development disclosed herein surprisingly lowers the occurrance of clustering of reducible iron-containing material in direct reduction furnaces. Summary of the Invention In one embodiment, the instant invention is a method to lower the incidence of clustering of reducible iron-containing agglomerates during the direct reduction of the iron in said material, said method comprising contacting the agglomerates with a cluster-abating effective amount of a dispersion of a particulate material, said particulate material being substantially non-hardening in the presence of water, wherein said contacting occurs prior to said direct reduction. Another embodiment comprises contacting the reducible iron-containing material prior to the direct reduction thereof with a cluster-abating effective amount of a dispersion which comprises at least one fluxing agent and at least one particulate material which is substantially nonhardening in the presence of water. In another embodiment, the instant invention involves contacting a reducible iron-containing material prior to the direct reduction thereof with cluster-abating effective amount of a dispersion which comprises at least one aluminium-containing clay. In yet another embodiment, the instant invention involves contacting a reducible iron-containing material with a dispersion of certain particulate material(s) by dipping or spraying. The current invention is also directed to the reducible iron-containing materials which have been treated by the methods of this invention. Detailed Description of the Invention The current invention relates generally to solving the problem of clustering of reducible iron-containing material during direct reduction of such material. The method comprises contacting agglomerates comprising reducible iron-containing material with a cluster-abating effective amount of at least one of certain particulate materials prior to direct reduction. In another embodiment, the method comprises contacting the reducible iron-containing material with a cluster-abating effective amount of a dispersion which comprises at least one fluxing agent and at least one particulate material prior to direct reduction. In yet another embodiment, the process comprises contacting the reducible iron-containing material with a dispersion which comprises an aluminium-containing clay. Such decreased cluster formation fosters more efficient and/or effective operation of the direct reduction furnace by allowing, for example, higher operation temperatures, increased through-put, etc. The reducible iron-containing material of the instant invention may be in any form that is typical for processing through a direct reduction furnace. For non-limiting example, the reducible iron-containing material may be agglomerated (e.g. pelletized, briquetted, granulated, etc.) and/or in natural virgin form (e.g. lump ore, fine ore, concentrated ore, etc.) In one embodiment, the reducible iron-containing material is in the form of pellets comprising binder and/or other typical additives employed in iron ore-pellet formation. For non-limiting example, such binders may be a clay, such as bentonite, montmorillionite, etc.; a water-soluble natural polymer, such as guar gum, starch, etc.; a modified natural polymer, such as guar derivatives (e.g. hydroxypropyl guar, carboxymethyl guar), modified starch (e.g., anionic starch, cationic starch), starch derivatives (e.g., dextrin) and cellulose derivatives (e.g., hydroxyethyl cellulose, carboxymethyl cellulose, hydroxypropyl cellulose, methyl cellulose, etc.); and/or a synthetic polymer (e.g., polyacrylamides, polyacrylates, polyacrylamide polyacrylate copolymers, polyethylene oxides, etc.). Such binders my be used alone or in combination with each other, and with or without inorganic compounds including but not limited to activators such as alkali carbonates, phosphates, citrates, etc. The binder may also be supplied in the form of a binder composition. A binder composition is often comprised of a binder or modified binder containing by-products of the binder formation as well as desired additives. A particularly preferred binder or binder composition of the instant invention is comprised of an alkali metal salt of carboxymethyl cellulose (CMC). The binder or binder composition of an alkali metal salt of CMC may contain as by-products, for example, sodium chloride and sodium glycolate, as well as other polysaccharides or synthetic water-soluble polymers and other "inorganic salts" (for non-limiting example sodium carbonate, sodium citrate, sodium bi-carbonate, sodium phosphate and the like). A series of commercially available binders containing sodium carboxymethyl cellulose especially useful in the present invention is marketed by Dreeland, Inc. of Denver, Colorado, USA and Akzo Chemicals of Amersfoort, the Netherlands, under the trademark Peridur®. As typical composition additives may be mentioned, by non-limiting example, flux (e.g., limestone, dolomite etc.), minerals to improve metallurgical properties of the pellets (e.g. olivine, serpentine, magnesium, etc.), caustic and coke. Typical binders and additives, as well as the method of use of binders and additives are well-known in the relevant art and thus need no detailed explanation here. See, for non-limiting example, U.S. Patent Nos. 5,000,783 and 4,288,245. As used herein, "dispersion" means any distribution or mixture of fine, finely divided and/or powdered solid material in a liquid medium. The similar terms "slurry", "suspension", etc. are also included in the term "dispersion". The dispersions of the present invention may optionally employ a stabilizing system which assists in maintaining a stable dispersion and enhances adhesion of the particulate material to the reducible iron-containing material, e.g., agglomerates. Any conventionally known stabilizing system can be employed in this regard with the proviso that they assist in stabilizing the dispersion. Examples of such stabilizing systems include but are not limited to systems which employ dispersants, stabilizers or combinations thereof. Preferred dispersants include but are not limited to organic dispersants including out not limited to polyacrylates, polyacrylate derivatives and the like and inorganic dispersants including but not limited to caustic, soda ash, phosphates and the like. Preferred stabilizers include both organic and inorganic stabilizers including but not limited to xanthan gums or derivatives thereof, cellulose derivatives such as hydroxyethyl cellulose, carboxymethylcellulose, carboxymethylhydroxyethyl cellulose, ethylhydroxyethylcellulose and the like, guar, guar derivatives, starch, modified starch, starch derivatives and synthetic viscosifiers sucn as polyacrylamides, polyacrylamides/polyacrylate copolymers, mixtures thereof and the like, mixed metal hydrates, synthetic hectorites, highly purified sodium montmorillonites, etc. As used herein, a "particulate material being substantially non-hardening in the presence of water" is a divided, finely divided and/or powdered material capable of forming a dispersion in a liquid medium and is substantially inert to hardening when mixed with water, unlike, for non-limiting example, portland cement. In a preferred embodiment, the particulate material is comprised of aluminum and/or an aluminum source and/or aluminum-containing compound, such as, for non-limiting example, bauxite and bentonite. More preferably, the particulate material is a bauxite and/or an aluminum-containing clay. Examples of aluminum-containing clays which are employable in the context of the present invention include but are not limited to bentonite, the kaolin minerals such as kaolinites, dickites, nacrites, halloysites and the like, serpentine clays such as lizardite, antigorite, carlosturanite, anestite, cronstedite, chamosite, berthierine, garnierite and the like, nodular clays, burleyflint clay, burley and diaspore, zeolite, pyrophyllites, smectite minerals such as montmorillorites, beidellites, nontronites, hectorites, soponites, sauconites volkhonskoites, medmontites, pimelites and the like, illites, glauconites, celadonites, chlorites such as clinochlores, chamosites, nimites, bailychlores, donbassites, cookites, fosterites, sudoites, franklinfurnacecites, and the like, vermiculites, palygorskites (attapulgites), sepiolites, mixed layer mineral clays, amophous and miscellaneous clays such as allophanes and imogolites, and high alumina clays such as diaspore clays, boehmite clays, gibbsite clays, cliachites, bauxite, bauxitic clays and gibbsitic or bauxitic kaolines. Alternatively, synthetic sodium aluminum silicates can be beneficially utilized. The particulate materials can be employed in either the hydrated or unhydrated forms. The size of the particulate material in the dispersions of the current invention is determined by the type of particulate material and its ability to form a dispersion in the medium selected. Thus, it may be said that, in general, the average size of the particulate material will be in the range of, for non-limiting example, below about 1 millimeter, typically in the range of about 0.01 microns to about 500 microns and more typically below 250 microns and, most typically in the range of about 50 microns to about 150 microns. More preferrably, the average particulate size is in the range of 0.05 to 100 microns. However, as explained above, the size of the particulate material will vary depending on many factors, but is well-known to person skilled in the art. Any fluxing agents conventionally employed in iron and steelmaking can be utilized in the dispersion of the present invention. Preferrably, lime-bearing materials are employed as fluxing agents. Non-limiting examples include lime-, calcium- and/or magnesium-bearing materials, dolomite, olivine, fosterite, limestone and the like. The dispersion of the present invention may also contain various materials and/or additives which are conventionally employed to improve the metallurgical properties of the pellets. Non-limiting examples include olivine, serpentine, magnesium, caustic, coke and the like. Again, the particle size of this material should be in the same range as that of the particulate materials. In carrying out the method of the instant invention, various techniques may be used to contact the reducible iron-containing material with the particulate material. The methods preferrably employed involve forming a dispersion (slurry, suspension etc.) of the particulate material and, if present, fluxing agent. Such dispersions, suspensions and/or slurries are formed with the aid of a liquid medium, for non-limiting example, water, organic solvents, solutions/dispersions of water-soluble/water-dispersible polymer(s) in water (e.g. to enhance dispersion), etc. The reducible iron-containing material is then contacted with the resulting dispersion, suspension and/or slurry. Such contacting may take place by, for example, spraying and/or dipping, and further, it may be partial or complete. For example, if such contacting is accomplished by dipping, the reducible iron-containing material may be partially dipped or completely immersed. In any event, the reducible iron-containing material may be contacted with a dispersion of particulate material(s) described herein at any time prior to direct reduction. For example, if the reducible iron containing material is provided in the form of pellets, the dispersion may be applied to either green or fired pellets. The "cluster-abating effective amount" will vary depending upon numerous factors known to the skilled artisan. Such factors include, out are not limited to, the type of reducible iron-containing material, as well as its physical form, moisture content, etc., the specific particulate material employed, as well as its form and other physical characteristics, the dispersion medium (e.g. water, alcohol, etc.), the concentration of particulate material in the dispersion medium, the operating conditions of the direct reduction furnace, etc. Though not limiting, a cluster-abating effective amount of a particulate material will typically be above about 0.01 wt.% based on the dry weight of the reducible iron-containing material after contact with the particulate material. Preferrably, the particulate material is present in the range of about 0.01 wt.% to about 2 wt.%. A typical dispersion will contain from about 1 to 80 wt.% particulate material, the remainder being the dispersion medium, e.g. water. In the case that bauxite is employed as a particulate material, a typical aqueous dispersion will be in the range of about 1 wt.% to about 80 wt.% solid material in water, and preferably 5 wt.% to 40 wt.%. Depending on contact conditions, the bauxite will be present on the reducible iron-containing material in the range of about 0.01 wt.% to about 1 wt.%. If bentonite is used as a particulate material, a typical aqueous dispersion will be in the range of about 1 wt.% to about 70 wt.%, and preferably 5 wt.% to 15 wt.%. Again depending on contact conditions, the bentonite will be present on the reducible iron-containing material containing in the range of about 0.1 wt.% to about 2 wt.%. A typical kaolin dispersion will contain from about 1% to 80% solid material in the dispersion medium e.g. water. Again, depending on contact conditions, the amount of kaolin deposited on the reducible iron-containing material will be in the range of about 0.1 wt.% to about 2 wt.%. When the dispersion of the present invention comprises particulate material(s) and fluxing agent(s), the "cluster abating effective amount" of dispersion will generally comprise particulate material in the range of from about 0.01 % to 2 % by weight based on the dry weight of the reducible iron-containing material after contact with the particulate material, and from about 0.01 to 15 wt.% or still more preferred, 1 to 6 wt.% fluxing agent based on the dry weight of the reducible iron-containing material after contact with the particulate material. The ratio of particulate material to fluxing agent in the dispersion will generally be in the range of from about 100:1 to 1:100. A preferred ratio of particulate material to fluxing agent is from about 1:10 to about 10:1 with a ratio of 1:5 to 5:1 being still more preferred. A typical dispersion will be a 1% to 80% dispersion with the ratio of particulate material to fluxing agent being in the range of 1:3 to 3:1. The invention is further described by the following non-limiting examples. Examples Reducible iron-containing pellets were prepared from iron ore concentrate admixed with 0.2 wt.% bentonite, 1.5 wt. dolomite and 0.06 wt. % Peridur® 230 binder (a sodium carboxymethyl cellulose-containing binder available from Dreeland, Inc. of Denver, Colorado, USA and Akzo Chemicals of Amersfoort, the Nether-lands). Procedures for such iron ore pellet formation are well-known to the skilled artisan, as, for example, demonstrated by European Patent Application EP 0 541 181 A1, EP 2 225 171 A2, US Patent No. 4,288,245, and the references cited therein. Accordingly, the detailed procedure need not be recited here. The formed green ball pellets were fired at about 1300°C. Portions of the fired pellets were then seperately contacted with dispersions of various particulate materials. For each particulate material dispersion tested, a sample of 2 kg of the above-described fired pellets was dipped in a 10% aqueous dispersion of the relevant particulate material for approximately 2 seconds, then dried at 105°C, leaving a deposit of about 0.05 wt.%. As indicated on Table I, bauxite, bentonite and Portland cement were tested as particulate materials. Also, an additional sample of 2 kg of the above-described fired pellets, identified as "Control", was subjected to no further treatment prior to direct reduction. Each pellet sample was separately subjected to a reduction temperature of 850°C (Examples 1-5) or 900°C (Examples 6 and 7). The reduced pellets were then subjected first to a "sticking tendency" test (to determine their tendency to cluster) and then to crushing strength test. The "sticking tendency" test was performed by dropping the reduced pellets from a height of one (1) meter. After each multiple of 5 drops (i.e., 5, 10, 15 and 20) the "clustered" pellets (a group of two or more pellets stuck together) and the "unclustered" pellets (single pellets) were weighed. The unclustered pellets were removed before the next series of 5 drops. The crushing strength was determined using the procedure of ISO 4700, with the exception that ISO 4700 prescribes oxidized pellets and here reduced pellets were tested. The results are reported in Table I. The foregoing examples have been presented to provide an enabling disclosure of the current invention and to illustrate the surprising and unexpected superiority in view of known technology.

Claims: A method to lower the incidence of clustering of reducible iron-containing agglomerates during the direct reduction of the iron in said agglomerates, said method comprising contacting the reducible iron-containing agglomerates with a cluster-abating effective amount of a dispersion comprising an aluminium-containing particulate material, said particulate material being substantially non-hardening in the presence of water, said contacting occuring prior to direct reduction. The method of claim 1 wherein the iron-containing agglomerates further contain at least one fluxing agent. The method of claim 1 or 2 wherein the aluminum-containing particulate material has an average particle size of less than about 250 microns. The method of any one of claims 1-3 wherein the aluminium-containing particulate material is bauxite or an aluminium-containing clay. The method of claim 4 wherein said aluminum-containing clay is selected from the group consisting of bentonite, kaolinite, attapulgite, dickite, nacrite, halloysite, pyrophyllete, montmorillonite, chlorite, hectorite, saponite, kaolin, sodium aluminum silicate, and mixtures thereof. The method of any one of preceding claims 1-5 wherein said iron-containing agglomerates are in the form of pellets, briquettes or granulates. The method of any one of claims 2-6 wherein said fluxing agent is a lime-bearing material. The method of claim 7 wherein said fluxing agent is selected from the group consisting of lime, hydrated lime, limestone, dolomite, and mixtures thereof. The method of any one of claims 1-8 wherein said dispersion additionally comprises at least one additive selected from the group consisting of olivine, serpentine, magnesium, caustic, coke, and mixtures thereof. The method of any one of claims 1-9 wherein said dispersion contains 1% to 80% by weight of particulate material. The method of any one of claims 2-10 wherein the dispersion contains at least one particulate material and at least one fluxing agent in a ratio of from about 1:5 to 5:1.

Inventors: STEEGHS HARRY R G, STEEGHS, HARRY R.G.
Applicants: AKZO NOBEL NV, AKZO NOBEL N.V.
Application year: 1994
Main classification: C21B13
IPC codes: C21B13, C21C5, C21B11